Cucumber vein yellowing virus (CVYV) is widespread in cucurbits in the Middle East. CVYV has filamentous particles and is transmitted byBemisia tabaci by the semi-persistent mode. It has not yet been assigned to a specific genus or family. Ultramicroscopic observations revealed numerous cylindrical cytoplasmic inclusions in melon and cucumber cells infected by CVYV isolates from Israel and Jordan. Depending on the section orientation, the inclusions appeared as pinwheels or as bundles. In addition, a 1n9 kb DNA fragment was amplified by RT-PCR from CVYV-infected plant extracts using primers designed to detect all potyvirids. Sequence comparisons with the amplified fragment indicated that CVYV is more closely related to Sweet potato mild mottle virus than to any other virus in the family Potyviridae. These results suggest that CVYV can be considered as a tentative new member of the genus Ipomovirus, family Potyviridae.Cucumber vein yellowing virus (CVYV) causes a severe disease of cucumbers and other cucurbits in the Oriental Mediterranean Basin (Cohen & Nitzany, 1960 ;Harpaz & Cohen, 1965 ;Al-Musa et al., 1985 ;Yilmaz et al., 1989). CVYV is reported to have rod-shaped particles, 740-800 nm long with a diameter of 15-18 nm (Sela et al., 1980). The virus is readily transmitted mechanically and by the whitefly Bemisia tabaci by the semi-persistent mode (Harpaz & Cohen, 1965 ;Mansour & Al-Musa, 1993). Due to the instability of CVYV particles, difficulties have been encountered in obtaining purified virus preparations (Sela et al., 1980 ;Mansour & Hadidi, 1999) ; therefore, very little is known of the biophysical Author for correspondence : Herve! Lecoq.Fax j33 4 32 72 28 42. e-mail Herve.Lecoq!avignon.inra.frThe GenBank accession number of the sequence reported in this paper is AF233429. and biochemical properties of CVYV and the virus is still unclassified (Brunt et al., 1996 ;Lecoq et al., 1998). However, Sela et al. (1980) have reported that the CVYV coat protein (CP) has a molecular mass of 39 kDa and that the viral nucleic acid is a double-stranded DNA, suggesting that CVYV could be a member of a new virus family.In order to investigate the taxonomic position of CVYV further, cytopathological, serological and molecular studies were conducted. Cucumber (Cucumis sativus cv. Beit Alfa) and melon (Cucumis melo cv. Ve! drantais) plants were inoculated mechanically with the CVYV type strain from Israel (CVYVIsr) or with a CVYV isolate from Jordan (CVYV-Jor) and were kept subsequently in independent screened cages maintained in an insect-proof greenhouse. The two strains induced similar vein-clearing symptoms in cucumber and melon, but CVYVJor caused a more severe stunting in cucumber.For cytological studies, leaf pieces 1 mm across were collected from symptomatic young leaves 3-4 weeks after inoculation and similar samples from healthy plants were used as controls. Samples were fixed with glutaraldehyde, post-fixed with osmium tetroxide and embedded in araldite CY212 (Agar Scientific) (Dele! colle, 1978). Thin sectio...
This study was conducted to determine the effect of two potyviruses, onion yellow dwarf virus (OYDV) and leek yellow stripe virus (LYSV), on the symptoms, growth, and potential yield loss of garlic (Allium sativum). For 2 consecutive years, the impact on leaf length, pseudostem diameter, and bulb weight was evaluated after mechanical inoculation of cultivars Messidrome, Germidour, and Printanor, the three main garlic cultivars grown in France. The reduction in bulb weight due to OYDV ranged from 39% for Germidour to about 60% for the two other cultivars. For LYSV, the reduction in bulb weight was less on Messidrome (17%) and Germidour (26%) than on Printanor (54%). Coinfection with both viruses further reduced growth and bulb weight. When cloves originating from bulbs infected by each virus alone or a mixture of both viruses were planted, results indicated that such chronic infection induced further yield reduction. An assay designed to evaluate the role of LYSV inoculation date on yield revealed that yield losses were the lowest for late-season infections. However, yield loss was greater than 30% when the inoculation was performed at the end of April, the time when natural contamination generally occurs in southern France. A comparison of the impact of mixed infections of OYDV and LYSV from different origins suggested that the isolates did not differ significantly in their effects on yield loss.
A potyvirus (Su-94-54) was isolated from a naturally infected snake cucumber (Cucumis melo var. flexuosus) plant with severe mosaic and leaf deformation symptoms collected in Eastern Sudan. This isolate has a host range limited to cucurbits and is serologically distantly related to Moroccan watermelon mosaic virus (MWMV) and to Papaya ringspot virus (PRSV). Coat protein sequence analysis of Su-94-54 and MWMV and comparison with other potyviruses indicate that Su-94-54 is more closely related to MWMV than to any other potyvirus. Based on the amino acid sequence identity in the core part of the coat protein with MWMV (86%), this isolate could be regarded as a distinct species. However, because of biological, cytological, and serological affinities with MWMV, we propose that this isolate be considered as a strain of MWMV, possibly an evolutionary intermediate between MWMV and PRSV, until more is known on the structure of the PRSV subgroup within the genus Potyvirus.
The full-length nucleotide sequence of the genomic RNA of a new cytorhabdovirus infecting lettuce was determined. Six open reading frames were found in the antigenomic sequence of the 12,926-nt negative-sense viral RNA genome. The genomic organisation was similar to that of lettuce necrotic yellows virus (LNYV), the type member of the genus Cytorhabdovirus: 3'-N-P-3-M-G-L-5', where N is the capsid protein gene, P the putative phosphoprotein gene, 3 a gene coding for a putative protein of unknown function, M the putative matrix protein gene, G the glycoprotein gene, and L the putative polymerase gene. Amino acid sequence comparison with the corresponding sequences of other rhabdoviruses revealed the closest relationship to LNYV, with identities ranging from 41% for the matrix proteins and 65% for the L polymerase proteins. These results indicate that this virus may be a member of a new cytorhabdovirus species, for which the name Lettuce yellow mottle virus (LYMoV) is proposed.
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